The objectives of this work are to: 1. Determine if the new aldehyde dehydrogenase (AlDH) isozymes generated during 2-acetylaminofluorene-induced hepatocarcinogenesis are the result of (a) derepression of gene(s) for AlDH nor normally expressed in rat liver or (b) gene derepression and epigenetic modification of newly synthesized and/or preexisting AlDH monomers. 2. Determine whether the expression of the hepatoma-specific aldehyde dehydrogenase phenotype is (a) the result of altered liver metabolism including a rearrangement of gene expression and/or regulation due directly to administration of carcinogen or (b) the result of transformation-associated stable changes in the cells affected by carcinogen.